Correlation of serum leptin with levels of hemoglobin in hemodialysis.

To examine the association of serum leptin level with anemia in hemodialysis, we investigated 36 patients (males: 21, diabetics: 11) under regular hemodialysis. For patients, complete blood counts, iron profile, serum leptin, and adequacy of hemodialysis were assessed. In this study a significant correlation of serum leptin with level of hemoglobin and body mass index was detected. An association between serum leptin and total iron binding capacity was observed. No correlation of serum ferritin with leptin level was seen. Our findings attest previous findings showing that greater serum leptin levels are associated with greater hemoglobin levels.


Introduction
Recent investigations have shown that leptin is cleared principally by the kidney. Therefore, serum leptin concentrations are increased in patients with chronic kidney disease and those undergoing maintenance dialysis (1)(2)(3). It has been thought that high serum leptin level may contribute to uremic anorexia and malnutrition (3)(4)(5). Serum leptin is generally elevated in chronic kidney disease and hemodialysis. Recent studies in dialysis patients suggest a paradoxically inverse relationship between elevated serum leptin and markers of nutritional status, a finding that is consistent with the theory of reverse epidemiology (2)(3)(4)(5)(6)(7)(8).
Usually chronic kidney disease patients develop anemia, which predominantly due to insufficient erythropoietin production by kidneys (9). Recently, studies have suggested a role for leptin in early stage of erythropoiesis and leptin has been found to stimulate hematopoietic stem cells in vitro (6)(7)(8)(9)(10)(11).

Objectives
Studies regarding the association of serum leptin with anemia in regular hemodialysis patients are quiet scarce. The aim of this study was to determine whether hyperleptinemia correlated with anemia markers in hemodialysis patients.

Patients and Methods
This cross-sectional study was conducted on stable hemodialysis patients. We excluded patients who had active or chronic infection, and those using non-steroidal anti-inflammatory drugs (NSAID) or angiotensin converting enzyme (ACE) inhibitors.

Laboratory assessments
Complete blood counts, serum iron, total iron binding capacity (TIBC), serum ferritin, serum creatinine, pre and post-dialysis blood urea nitrogen (BUN) was assessed. Blood samples were drawn after an overnight fast. Serum Leptin (normal range of values for males is 3.84 (1.79) and for females is 7.36 (3.73) ng/ ml) was measured by enzyme-linked immunosorbent assay (ELISA) method using DRG kits-Germany. To evaluate the efficacy of hemodialysis, the urea reduction rate (URR) was calculated from pre-and post-blood urea nitrogen (BUN) data (12). Body mass index (BMI) was calculated using the standard formula (post dialysis weight in kilograms/ height in square meters; kg/m 2 ) (13). Duration of hemodialysis treatment were obtained from the patients' records. The duration of each hemodialysis session was 4 hours.

Ethical approval
All patients signed the consent form for participation in this study. Research study was approved by the ethics committee of Shahrekord University of Medical Sciences, Iran.

Statistical Analysis
Statistical analysis was performed on total hemodialysis (HD), females, males, diabetic and non-diabetic populations separately. Data were expressed as the mean ± standard deviation (SD). Student's t-test was used to compare the study groups. Partial correlation and Pearson tests were used to evaluate statistical correlations. All statistical analyses were performed using SPSS (version 11.5). Statistical significance was determined at a p-value<0.05.

Results
There was 36 hemodialysis patients (15 females, 21 males) consisting of 25 (11 females, 14 males) non-diabetic patients and 11 (4 females, 7 males) diabetic hemodialysis patients. Table 1, shows the patients' data. The mean patients' age was 47 (17) years. The median value of serum leptin in the study patients was 5.75 ng/ml; the median values of serum leptin in the diabetic and non-diabetic groups were 8.3 and 4 ng/ ml, respectively. There was a significant positive correlation of serum leptin with hemoglobin levels (r= 0.36, p= 0.033). A significant positive correlation of serum leptin with BMI (r= 0.56, p< 0.001). There was no significant correlation between serum leptin and serum ferritin or total iron binding capacity in all patients or in the subgroups.

Discussion
In this study, we found a significant positive correlation between serum leptin and hemoglobin and body mass index. Tungtrongchitr et al, considered, 214 overweight patients without kidney failure (body mass index ≥25). They found a significantly higher serum leptin level, mean corpuscular hemoglobin concentration and mean corpuscular volume in the overweights, in comparison to the control subjects (14). Previous studies in hemodialysis patients indicated that individuals with high serum leptin levels were more likely to lose weight (15)(16)(17). However, more recent studies of hemodialysis patients suggest a paradoxically inverse association between higher serum leptin and markers of nutritional status (6,7), a finding that was consistent with the theory of reverse epidemiology (8). Leptin is similar to serum albumin, which is a negative acute phase reactant in end-stage kidney failure patients (7). A study conducted by Dedoussis et al. on 40 beta-thalassemia patients found that leptin might play some role in hematopoiesis (18). Kokot et al. assessed the influence of 12 months of Eprex therapy on plasma leptin in 15 hemodialysis patients and showed significantly lower leptin level after 3, 6, and 12 months of Eprex therapy as compared to the beginning of the study (19). Of interest, hemodialysis patients with a high body mass index Hyperleptinemia may reflect better nutritional status and Eprex response in hemodialysis patients. Increasing energy intake corrects erythropoiesis, which may be partly mediated by an increase in serum leptin levels (24). Increased leptin levels could both improve the erythropoietic response and reduce Eprex dose when greater body fat mass is achieved by caloric supplementation (24). While, leptin is considered an "appetite inhibitor" in the general population, its role in end-stage kidney failure patients is somewhat unconventional. Serum leptin is generally elevated in end-stage kidney failure patients, but this has not been observed in anorexia. Leptin has been shown to act synergistically with erythropoietin to stimulate end-stage colony-forming-unit erythroid in humans (25).

Conclusion
In this study, we detected a positive correlation between serum leptin level with body mass index and hemoglobin level, which supports the theory of a reverse epidemiological role for leptin in the regular hemodialysis patients.

Authors' contributions
MRK and HN wrote the manuscript equally.

Conflict of interests
The authors declared no competing interests.

Ethical considerations
Ethical issues (including plagiarism, misconduct, data fabrication, falsification, double publication or submission, redundancy) have been completely observed by the authors.

Funding/Support
This study was supported by a grant from Shahrekord University of Medical Sciences.